It is well known that drag of a ship or submarine through the water can be significantly reduced by ejecting a polymer solution over the exterior of the vessel. Polymer solutions must be mixed in extensive quantities in order to achieve this purpose. Present methods for mixing polymer solutions normally use either a powder mixer or a venturi-type slurry dispenser. In the powder mixer a dry polymer powder is metered into a large surface area of water, after which the powder and water are turbulently mixed to provide the polymer solution. This type of mixing tends to form gelatinous lumps in the polymer solution, and continuous maintenance and cleaning are required. Further, this type of mixing is not suitable for shipboard or submarine use because air, usually atmospheric pressure, is required and this pressure is less than the hydrostatic pressure at the polymer solution outlet over the exterior surface of the vessel.
Present day slurry dispensers operate by injecting a highly viscous slurry into a highly turbulent stream of water. The slurrly is typically pumped or forced through a small orifice, usually about 1/8" in diameter, into the throat of a venturi dispenser. Mixing is accomplished by maintaining a large difference in velocity between the slurry and the water. This dispenser, which has mixing capabilities of around 600 gpm, can operate in a submerged environment since no air is required. However, this type of mixing has several serious drawbacks, a primary one being clogging at the orifice due to synaresis which is a phenomenon where the powder separates from the liquid carrier when accelerated because of constrictions and results in deposits at the constrictions. This type of dispenser also requires a very clean slurry and a shut-off valve for the slurry at the throat of the venturi dispenser. Also, it can be visualized that because of the localized injection of the slurry the dispersion thereof will be less than that desired. Both the powder mixer and the presently existing slurry dispensers are large units and somewhat expensive to fabricate.